1.Field of the Invention
This invention relates to methods and means for positioning surface mounted electronic components, especially fine pitch components, on the surface of a printed wiring board. More particularly, it is concerned with methods and means which employ surface tension effects for precisely positioning electronic components on a printed wiring board during the assembly process.
2. Prior Art
Fine pitch surface mounted electronic components with lead spacing of 0.040" or less offer a number of advantages over conventional 50 mil-spaced components in addition to small size. These include, among others, increased input and output handling capacity, enhanced throughput speed, relatively low cost, and the potential for substantial reductions in the cost of integrated systems adapted to utilize fine pitch technology.
Unfortunately, the characteristics that provide these advantages, small size, high lead count and close lead spacing, are the source of a number of significant disadvantages as well. By way of example, lead-to-pad misregistration, solder bridging, and slumping, all relatively minor, fairly easily avoided annoyances with 50-mil on center components, become major problems when pad spacing gets down to 40-mils or less.
To some extent these problems can be overcome or alleviated by conventional means, such as taking pains to improve the quality of the circuit artwork, providing for greater consistency in solder plating on the contact pads, paying special attention to circuit and pad geometry, exercising more effective control over the solder reflow process, and the like. But greater precision, special handling and enhanced quality control are costly. Ultimately, the conflicting demands of miniaturization and cost-effectiveness can be satisfied only by improving the accuracy with which the components are positioned on the board surface.
Heretofore, the usual approach to improving placement accuracy has been to design ever more sophisticated pick-and-place machines. Computer controlled and provided with remote monitors and elaborate robotics, these high output precision machines are so costly to manufacture, complicated to use and difficult to maintain and repair they are for all practical intents and purposes out of the reach of many potential users. The subject invention represents a totally different approach.
One of the objects of the invention is to provide a novel method and a family of unique devices for accurately positioning surface mounted components, particularly fine-pitch components, on the board surface without need for elaborate high precision pick-and-place equipment.
Another object is to provide a method and means for accurately positioning components, which employ surface tension principles in place of customary prior art pick-and-place techniques.
Yet another object is to provide a method and means for positioning surface mounted components, that require a minimum of human intervention.
Still another object is to furnish a family of high-precision positioning devices that are readily adaptable for use with a variety of surface mounted components.
A further object is to provide a line of such devices that are inexpensive to manufacture, simple to use and substantially free from maintenance and repair needs.
Other objects will become apparent from the following summary of the invention and detailed description of several of its preferred embodiments.